This application claims benefit of Japanese Application No. 2001-377613 filed Dec. 11, 2001, the contents of which are incorporated by this reference.
1. Field of the Invention
The present invention relates to a lens barrel, and more particularly, to a lens barrel in which a plurality of optical elements are fixed and held with a high accuracy and which has a high optical performance.
2. Related Background Art
Conventionally, a lens barrel for holding a photographing optical system used in a photographing apparatus (camera) and the like is ordinarily formed of plastic parts and the like molded by injection molding and so on.
Here, the lens barrel is arranged such that a plurality of optical elements such as lenses and the like constituting the photographing optical system are held by frame members, support members, and the like (hereinafter, simply referred to as frame members and the like) corresponding to the respective optical elements, and these frame members and the like are relatively moved in a direction along an optical axis.
In this case, the optical axes of the plurality of optical elements constituting the photographing optical system must be in agreement with each other.
For example, when the respective optical axes of a plurality of optical elements held by a single frame member and the like or the respective optical axes of a plurality of optical elements held by a plurality of frame members and the like are not in agreement with each other, an optical performance cannot be maintained and an excellent subject image cannot be formed.
Accordingly, when the lens barrel is manufactured, it is a very important problem to secure the accuracy of parts such as the respective frame members and the like constituting the lens barrel. Specifically, surfaces for prescribing the positions of the respective optical elements held by, for example, the frame members, that is, lens position prescribing surfaces in the radial direction and the optical axis direction of the optical elements (hereinafter, simply referred to as position prescribing surfaces) must be accurately prescribed.
For this purpose, an arrangement shown in, for example, FIG. 11 is used in a conventional lens barrel.
FIG. 11 is an enlarged main portion sectional view showing only an upper half portion of the optical elements about the optical axis thereof by taking out a frame member constituting a part of the conventional lens barrel and the optical elements held by the frame member. Further, FIG. 12 is a sectional view showing a part of molds for injection molding the frame member shown in FIG. 11, the sectional view showing a region corresponding to FIG. 11.
As shown in FIG. 11, the frame member 116 constituting a part of the conventional lens barrel is composed of a frame portion 116a for fixing and holding the plurality of optical elements and a support portion 116b for holding the frame portion 116a. 
The frame portion 116a is formed to hold a front lens group 156a as a first lens and a rear lens group 156b as a second lens, respectively.
In this case, the position of the front lens group 156a in a direction along an optical axis O is prescribed by a position prescribing surface, which is denoted by a reference numeral 116c, of the frame portion 116a. Further, the position of the front lens group 156a in a diameter direction is prescribed by a position prescribing surface, which is denoted by a reference numeral 116d, of the frame portion 116a. 
In contrast, the position of the rear lens group 156b in the direction along the optical axis O is prescribed by a position prescribing surface, which is denoted by a reference numeral 116e, of the frame portion 116a. Further, the position of the rear lens group 156b in the diameter direction is prescribed by a position prescribing surface, which is denoted by a reference numeral 116f, of the frame portion 116a. 
To mold the frame portion 116a arranged as described above, the injection molding mold as shown in FIG. 12, that is, a first mold member 120 and a second mold member 121 are used.
Note that a line denoted by a symbol X in FIG. 12 shows a dividing position of the mold members 120 and 121.
In this case, the position prescribing surface 116c (the optical axis direction) in the frame portion 116a is formed by a surface, which is denoted by a reference numeral 121c, of the second mold member 121. Further, the position prescribing surface 116d (the diameter direction) in the frame portion 116a is formed by a surface denoted by a reference numeral 121d of the second mold member 121.
In contrast, the position prescribing surface 116e (the optical axis direction) of the frame portion 116a is formed by a surface, which is denoted by a reference numeral 121e, of the second mold member 121. Further, the position prescribing surface 116f (the diameter direction) of the frame portion 116a is formed by a surface, which is denoted by a reference numeral surface 121f, of the second mold member 121.
The plurality of optical elements (156a, 156b) are sequentially inserted into frame portion 116a arranged as described above from the same direction, that is, from the side of a rear opening 116g and assembled.
Accordingly, in the molds (120, 121) used when the frame portion 116a in the lens barrel is molded, all the position prescribing surfaces (116c, 116d, 116e, 116f) of the plurality of optical elements (156a, 156b) are molded by the single mold member 121. In contrast, in manufacture, the dimensional accuracy of parts can be easily increased by molding them in the same molding member. From the above arrangement, in this example, the frame portion 116a, which can prescribe the positions of the respective optical elements (156a, 156b) easily with a high accuracy, can be realized.
As described above, the frame member (116) of the lens barrel, which is to be molded from the molds (120, 121) of a mode shown in FIG. 12, is assembled by sequentially inserting the plurality of optical elements from the same direction with respect to the frame member, that is, from the rear opening 116g into the inside of the frame portion 116a. 
Therefore, as shown in FIG. 12, the diameter Rb of the surface 121f of the second mold member 121 corresponding to the position prescribing surface 116f of the other rear lens group 156b in the diameter direction must be definitely set larger than the diameter Ra of the surface 121d of the second mold member 121 corresponding to the position prescribing surface 116d of the one front lens group 156a in the diameter direction (Ra less than Rb).
As a result, a step denoted by a reference numeral d0 (=(Rbxc2x7Ra)/2) is arisen between the position prescribing surfaces 116d and 116f in the diameter direction, as shown in FIG. 11.
Further, in the example shown in FIG. 11, since the lens group 156a must be fixed to the frame member 116, the front lens group 156a is fixed to the frame member 116 on, for example, the outer peripheral portion of the lens group 156a through an adhesive 200. Thus, in this case, a bonding portion where the lens group 156a is fixed must be interposed between the lens groups 156a and 156b. 
That is, the step shown by the reference numeral dO must be formed so as to secure an adhesive reservoir for applying the adhesive 200, thereby the diameter of the frame portion 116a is increased.
Note that, in the case shown in FIG. 11, the lens group 156b is also fixed to the frame member 116 on the outer peripheral portion thereof through an adhesive 201.
From the above arrangement, in the lens barrel of the mode described above, the dimension in the diameter direction of the frame portion 116a is increased from the necessity for securing the position prescribing surfaces of the respective optical elements, from which a problem is arisen in that the frame portion 116a and, the mold members 121, 122 for molding it are increased in size.
Further, in the lens barrel of the mode described above, the position prescribing surfaces of the respective optical elements in the direction along the optical axis cannot be disposed at positions where they confront with each other, from which a problem is also arisen in that it is difficult to sufficiently secure a dimensional accuracy of the interval between adjacent optical elements. Further, when it is intended to interpose an aperture portion between the lens groups 156a and 156b in the lens barrel of the mode described above, the diameter of the opening of the aperture portion is smaller than the outside diameter of the lens group 156a. Thus, it is difficult to form the aperture portion integrally with the frame member 116 from the view point of assembly, from which a problem is arisen in that the lens barrel of the mode described above has a structure requiring a different member.
A feature of the present invention is to provide a lens barrel capable of holding a plurality of optical elements constituting a photographing optical system while securing a high relative coaxial accuracy between the optical elements and a high dimensional accuracy between the elements and capable of contributing to the further miniaturization of a camera and the like.
To briefly describe, a first invention is a lens barrel having lens a holding frame for holding a plurality of lenses, the lens barrel being characterized by including a first lens, a second lens, a lens holding frame holding the first and second lenses, having a first opening disposed at one end in correspondence to the first lens, and having a second opening disposed at the other end in correspondence to the second lens, first abutment portions prescribing the position of the first lens in an optical axis direction on the first opening side and disposed at a plurality of positions around the inner periphery of the lens holding frame, a second abutment portion prescribing the position of the second lens in the optical axis direction on the second opening side, first engagement portions disposed at a plurality of positions around the inner periphery of the lens holding frame on a side nearer to the first opening than the first and second abutment portions and engaged with the first lens, and a second engagement portion disposed around the inner periphery of the lens holding frame on a side nearer to the second opening than the second abutment portion and engaged with the second lens, wherein the first engagement portions and the first abutment portions are disposed at different positions in the circumferential direction of the lens holding frame.
Further, a second invention is a lens barrel characterized by including a first lens, a second lens, a lens holding frame holding the first and second lenses, having a first opening disposed at one end in correspondence to the first lens, and having a second opening disposed at the other end in correspondence to the second lens, a first engagement portion disposed to the lens holding frame on the first opening side thereof and engaged with the first lens, a second engagement portion disposed to the lens holding frame on the second opening side thereof and engaged with the second lens, wherein the first and second engagement portions are molded by the same metal mold.
Then, a third invention is a lens barrel including a first lens, a second lens the diameter of which is larger than that of the first lens, and an approximately cylindrical lens holding frame holding the first and second lenses, having a first opening disposed at one end in correspondence to the first lens, and having a second opening disposed at the other end in correspondence to the second opening, wherein the lens holding frame is molded by a first metal mold on the first opening side and a second metal mold on the second opening side. Further, the lens barrel includes first abutment portions prescribing the position of the first lens in an optical axis direction on the first opening side, disposed at a plurality of positions around the inner periphery of the lens holding frame, and projecting toward the inner periphery of the lens holding frame, respectively and the first abutment portions are molded by the first metal mold. Then, the lens barrel includes a second abutment portion prescribing the position of the second lens in the optical axis direction on the second opening side, and the second abutment portion is molded by the second metal mold. Further, the lens barrel includes first engagement portions disposed at a plurality of positions around the inner periphery of the lens holding frame on a side nearer to the first opening than the first and second abutment portions, and engaged with the first lens, the first engagement portions being molded by the second metal mold. Further, the lens barrel includes a second engagement portion disposed around the inner periphery of the lens holding frame on a side nearer to the second opening than the first and second abutment portions and engaged with the second lens, and the second engagement portion is molded by the second metal mold. In the above arrangement, the first engagement portions and the first abutment portions are disposed at different positions in the circumferential direction of the lens holding frame.
These and other features and benefits of the present invention will be more apparent from the following detailed description.
According to the present invention, there can be provided a lens barrel capable of holding a plurality of optical elements constituting a photographing optical system while securing a pinpoint relative coaxial accuracy between the optical elements and a pinpoint dimensional accuracy between the elements and capable of contributing to the further miniaturization of a camera and the like.